We report our experience with 40 retrograde renal brush samples of pelvic-calyceal lesions with confirmatory tissue studies. On-site cytopathologic evaluation was performed in 38 of these specimens. The final histologic diagnoses included 24 cases of transitional cell carcinoma (TCC), 17 of which were low-intermediate grade tumors. All 24 cases were diagnosed cytologically as TCC (22), or as suspicious for TCC (2). Three cases classified as collecting duct carcinomas were resected; the cytologic specimens in 2 of these cases were interpreted as TCC, and one as reactive change. There were three renal cell carcinomas (RCC); cytologically, one was considered a papillary neoplasm, one suspicious for malignancy, and one as reactive. Two cases of atypical renal cysts were reported as suspicious for malignancy in both cytologic and histologic material. There was one case of metastatic colon carcinoma identified in the brush specimen. Finally, tissue studies in the remaining 7 cases showed reactive/inflammatory changes; however, four of the corresponding pelvic brush specimens were considered abnormal. A review of the above cases is reported with the objective of presenting the cytologic features seen in collecting duct carcinoma, low-intermediate grade TCC, and diagnostically difficult cases with cyto/histomorphologic discrepancies. The contribution of on-site assessment to diagnostic accuracy is also discussed.